Clarify SSO enforcement setting behaviour
What
Updates the description of the Enforce SSO setting based on the :enforced_sso_requires_session flag.
Why
Makes the current behaviour more clear until we enable the feature flag shortly.
Also helps with https://gitlab.com/gitlab-org/gitlab-ee/issues/13705, which was created to solve an overlapping problem.
Screenshot
Conformity
Edited by James Edwards-Jones